How Do You Flush a Spin-Down Sediment Filter, and How Often Should You Do It?

How do you flush a spin-down sediment filter?

You open the flush valve at the bottom of the clear bowl for a few seconds while the filter is under pressure, and let the water push the grit out. Rusco’s installation sheet calls it the purge valve and says exactly that: open it for a few seconds while the system is under pressure, and always close the valves slowly to avoid water hammer [1]. The same sheet calls purging the separated solids through that valve the primary way of cleaning the filter, done by hand or by an automatic valve the maker sells [1]. Those are one maker’s instructions, not necessarily the brand in the photo above.

iSpring’s manual for its spin-down models describes the same thing in its own words: make sure there is a reliable drain or a suitable container, turn the drain valve knob, and flush for about 30 seconds; its models with a scraper also have you turn the scraper knob three or four times while the water runs [3]. Rusco’s sheet speaks of pressure from a pump or a tank, because it is written with wells in mind [1]. Our reading: on city water the pressure comes from the main, and it does the same job.

Why it works is in the drawing below. Water enters the head and is set spinning around a cylindrical screen; the heavier particles are thrown outward and drop to the bottom of the bowl, where they collect right above the flush valve [5]. Opening the valve sends that pile out first.

How often should you flush a spin-down filter?

Whenever you can see sediment collecting in the bowl — there is no single interval, because it depends on how much grit your water carries. Rusco’s literature says the sediment is visible through the clear cover, indicating when the filter needs cleaning [2]. iSpring’s manual is the only maker’s document we read that puts a number on it: it recommends flushing at least once a week, for 30 seconds each time, depending on the incoming water, and elsewhere says the screen needs flushing at least once a month depending on water quality [3]. Boshart’s page on the difference between cartridge and spin-out filters gives no purge interval at all [5].

Our reading of those three: look at the bowl. If there is a visible layer at the bottom, flush it; if it fills up again within days, flush more often. A flush takes seconds, so there is little reason to let the layer build up.

How do I know my spin-down filter needs flushing?

Three signs, in the order you will usually notice them: grit sitting in the bottom of the clear bowl, weaker flow at the taps, and a screen that has turned green or brown. The first is the one Rusco designs the clear cover for [2].

For low flow, iSpring’s troubleshooting table lists two causes: an inlet valve that is not fully open, or a filter screen that is partly blocked — and the fix for the second is to flush the screen [3]. If flushing does not bring the flow back, the screen itself needs cleaning (below), and if that does not either, the cause is somewhere else in the house; our article on low water pressure goes through the usual suspects.

A green or brown screen is algae, covered in its own section further down.

Do I need to turn the water off to flush a spin-down filter?

No — to flush it, the water stays on; the pressure is what clears the bowl. Rusco says to open the purge valve while the filter is under pressure [1], lists “no downtime” among the filter’s features [2], and iSpring says its toggle lets trapped particles be flushed out without shutting down the water supply first [3].

Yes — to take the screen out. Rusco’s sheet says to shut off the water, relieve the pressure, then unscrew the clear cover [1]. Boshart’s cleaning page spells the same out: close the shut-off valve on the inlet side, open a faucet on the outlet side to relieve the pressure, and open the purge valve to drain the bowl before loosening it by hand [4]. If you are not sure which valve feeds the filter, our article on where the main water shutoff valve is shows how to find the house valve.

Where does the flush water go?

Into a bucket or a drain — somewhere safe for dirty water. Rusco’s sheet says the water purged through the valve must be drained to a safe place, asks for an air gap of about 1.5 to 2 inches between the flush valve, or any pipe on it, and the drain, and wants any line fitted after the valve to be flexible tubing or joined with a union, so it does not get in the way when the cover comes off for cleaning [1]. iSpring says to make sure there is a reliable drainage system before flushing, or to flush into a suitable container [3].

Our reading: for a filter at the water service outside, as in the photo at the top of this page, a bucket held under the valve is the simple answer. Never connect the valve straight into a drain pipe without that gap.

How do you clean the screen inside a spin-down filter?

Flushing clears the bowl; it does not always clear what has stuck to the screen. When it does not, the screen comes out. Boshart’s step-by-step for its spin-out filters [4], with Rusco’s and iSpring’s additions [1][3]:

• Close the shut-off valve feeding the filter, and open a faucet on the house side to relieve the pressure [4]
• Open the purge valve to drain the bowl, then unscrew the clear bowl by hand [4]; Rusco says its plastic parts are tightened by hand only, never with tools [1]
• Pull the screen straight down and out; wash it with warm soapy water and a soft brush, then rinse [4]. Rusco also says to brush the fine particles lodged in the screen with a soft brush [1]; iSpring says a brush or a vinegar soak, after 8 to 12 months of continuous use [3]
• Wipe the O-rings and their grooves clean and give them a light coat of silicone grease; Boshart specifies one that is FDA or NSF-61 approved [4], Rusco names silicone grease as the only lubricant to use on its O-rings [1]
• Put the screen back, screw the bowl on by hand, close the purge valve, turn the water back on and run water to a nearby drain for 5 minutes; then check for leaks with the filter under pressure [4]

Why is the screen in my spin-down filter turning green?

Because light is reaching the water through the clear bowl, and algae grows. Rusco says it plainly: a screen that turns green or brown is algae, caused by adding light to the water; it is not harmful to humans, but it looks bad and clogs the screen. Rusco’s answer is a cover that slips over the clear bowl and cuts out the sunlight, taken off when you check the filter, and it tells owners to ask for one if the filter is to be installed outside in the sun [1].

iSpring goes further for its own models: they are not to be installed outdoors and are to be kept away from direct sunlight [3]. Our reading: in Florida a filter at the water service is often outside, as ours in Dunedin is, so if the screen goes green, check what your maker says about sun and whether it sells a cover; then clean the screen as above.

How is a spin-down filter different from a cartridge filter?

A spin-down filter is flushed and its screen is reused; a cartridge filter is thrown away and replaced. Boshart explains that its spin-out filter has a purge valve for flushing sediment without taking anything apart, while a traditional cartridge works as long as the sediment load is not too heavy and has to be replaced on schedule [5]. Rusco’s screens are reusable elements, in polyester or stainless steel [2].

The two are often used together. Rusco’s sheet shows its spin-down filters as prefilters installed ahead of a cartridge filter to increase the lifespan of the cartridges [1]. What a cartridge’s micron rating means and when to change it is covered in our article on sediment prefilters and micron ratings, and where a sediment stage sits in a full treatment system is in why a softener needs a prefilter and a post-filter.

What this means in Dunedin, Clearwater and across Tampa Bay

The filter at the top of this page is ours. On 13 October 2026 we installed a whole-house 500-micron spin-down sediment prefilter at the water service of a home in Dunedin: a clear bowl with a flush valve at the bottom, connected with stainless flex connectors, a PVC riser with a ball valve, and CPVC into the house.

A filter at the water service treats all the water entering the house, so it is the one to keep flushed. If your spin-down filter is leaking at the bowl, will not clear when you flush it, or you would like one at your water service, call 727-470-7126.

FAQ

Sources

We review and cite. We do not reproduce a paper or a manual — follow the links for the originals.

1. [1]Spin-Down Filter installation sheet (cleaning, backflushing, Sun Shield) — Rusco, Inc. (copy hosted by FreshWater Systems)Manufacturer's manual · One maker’s instructions, not necessarily the brand we install. Two-page scanned sheet, undated. “Cleaning your filter” (English): open the purge valve for a few seconds while the system is under pressure from pump or tank; always close the valves slowly to avoid water hammer. “Sun Shield” (English): a green or brown screen is algae caused by adding light to the water; not harmful to humans, looks bad and clogs the screen; the Sun Shield slips over the clear cover and cuts out sunlight; slip it off to check the filter; ask for it if the filter is installed outside in the sun. “Step Down Filtration” (English): spin-down filters as prefilters before a cartridge filter to increase cartridge lifespan. The English cleaning/precautions panel is cut off in the scan, so these points were read in the sheet’s own Spanish and French versions: primary cleaning is purging separated solids through the flush valve while under pressure, manually or with the maker’s automatic valve; to clean the element shut off the water, relieve pressure, unscrew the clear cover, wash, brush lodged particles with a soft brush, silicone grease on O-rings, hand-tighten; purge water must drain to a safe place; 1.5–2 in air gap between flush valve/pipe and drain; line after the valve flexible or on a union; tools on plastic parts void the warranty; silicone grease (Dow 111) the only O-ring lubricant. Read 2026-11-09
2. [2]Spin-Down Sediment Filters — product brochure — Rusco, Inc.Manufacturer's manual · One maker’s literature, not necessarily the brand we install. Undated, hosted by a distributor. “Sediment is visible through the clear cover indicating when the filter needs cleaning”; sediment removed by opening the ball valve at the bottom of the filter cover; reusable polyester and stainless steel element screens; “No downtime”; centrifuge spin-down type separation; minimum flow rates for spin-down action; tools void warranty, hand-tighten only. Read 2026-11-09
3. [3]WSP-ARB / WSP-B Series User Manual, Ver. 07/2020 — iSpring Water Systems, LLC (copy hosted by The Home Depot) · 2020Manufacturer's manual · One maker’s instructions, not necessarily the brand we install. Particles can be flushed without shutting down the water supply; ensure reliable drainage before flushing or flush into a suitable container; turn the drain valve knob; scraper knob 3–4 turns while draining; recommend flushing at least once a week for 30 seconds, depending on incoming water; elsewhere ‘flush the filter screen at least once a month’ depending on water quality; after 8–12 months continuous use remove the mesh and brush or soak in vinegar; not to be installed outdoors, away from direct sunlight; troubleshooting: low outlet flow = inlet valve not fully open or screen partially blocked, flush the mesh. Read 2026-11-09
4. [4]How to Clean your Spin-Out Filter — Boshart Industries · 2025Manufacturer's manual · One maker’s instructions, not necessarily the brand we install. Dated 2025-12-19. Close the inlet-side shut-off valve; open a faucet on the outlet side to relieve pressure; open the purge valve to drain the bowl; loosen the clear bowl by hand; pull the 316 SS screen straight down; clean screen and housing with warm soapy water and a brush, rinse; optional bleach sanitising; lubricate O-rings with FDA or NSF-61 approved silicone grease; reinstall by hand; close purge valve, reopen inlet, run water to a nearby drain for 5 minutes; check for leaks under pressure. No cleaning interval given. Read 2026-11-09
5. [5]What is the difference between a traditional sediment filter & a spin-out sediment filter/separator? — Boshart Industries · 2023Manufacturer's manual · Maker’s support article, dated 2023-10-05. Spin-out filter: rapid spinning separates heavier particulate by centrifugal force; sediment drops into the lower chamber; purge valve allows quick flushing without disassembly. Traditional cartridge: performs well if the sediment load is not too heavy; must be replaced on a schedule. No purge interval given. Read 2026-11-09