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Old 11-23-2020, 05:29 PM   #1
Winnebago Camper
Join Date: Jun 2020
Posts: 13
check valve in drain?

Are there check valves in the sink drains in motor home drains? I have a 2015, Minnie Winnie 31K, that I've owned for 6 months. Several timespI've noticed the lavatory sink does not drain, at all. Most often, it drains fine. All or none and only the lavatory sink. Check valve, air lock? Any ideas? I have not taken the drain apart.


2015 Minnie Winnie 31K on 2014 E450
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Old 11-24-2020, 01:24 PM   #2
Winnebago Owner
Join Date: Oct 2019
Posts: 63
I know of no drains that have a checkvalve. Sounds to me that you either have a random blockage or a venting problem. I'd check the vent on the roof and make sure that you don't have an obstruction.
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Old 11-24-2020, 02:21 PM   #3
Join Date: Feb 2020
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Some motor homes don't have roof vents, they have air admittance valves usually located below the sink in the cabinet mounted on a short vertical pipe riser. For a sink they are usually 1-1/2" and have a large check valve flapper that lets air in to vent the sink drain but blocks anything going up and out.

Maybe the flapper gets stuck and that makes the sink air lock. Easy enough to replace if that is it. Amazon, Home Depot, Lowes or any hardware store has them.

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Old 11-24-2020, 04:20 PM   #4
2019 Winnebago Sunstar 27
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Join Date: Jul 2019
Posts: 54

You do have a "Trap-Waterless" fitted in the drain line of your lavatory.
Check out Sheet 2 of 4 here:
THis is installed versus the standard P Trap due to space and height limitations.

2019 27PE
Vancouver Island BC Canada
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Old 11-24-2020, 09:38 PM   #5
Ed & Lynn
Join Date: Oct 2018
Location: Central Oregon Coast
Posts: 70
Yes - as Lowdie24 said, there ARE trapless drain devices in use where P traps won't fit. I know that our previous Tiffin motor home had at least one in the shower drain..... sorta a rubberized thing that collapses to prevent backflow but allowed drain water through.
Ed & Lynn - on the Central Oregon Coast
Lily & Tyler - Bedlington Terriers
2018 Winnebago Fuse 23A
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Old 11-25-2020, 01:19 AM   #6
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Our 2016 Minnie Winnie 27Q has a P-trap on the lav sink. I'd first disassemble the P-trap to see if there is a blockage or maybe a restriction caused by a plug of hair/grease/soap.

If no obstruction is found, I'd replace the under-sink air vent. The thin rubber diaphragm inside it can and does deteriorate over time. It will be just under the bottom side of the countertop and possibly under the sink itself.

Replacement air vents are available at Home Depot for around $10.
2016 Minnie Winnie 27Q on a 2015 Ford E450 chassis. Retired U.S. Air Force. Living in Anchorage, Alaska
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