Shower Sump

Below Floor Rule 98B Shower Sump

One of the main reasons for taking on the Clipper project was to have a toilet and shower in our trailer. Our '48 Boles Aero is too small for such conveniences but we both feel they would make using the trailer a lot more attractive (the middle of the nights trips to a campground bathroom just aren't fun).

The Clipper has a very low roofline so there's really no extra room to elevate the shower to provide direct drainage to a grey water tank. To solve the problem I planned to borrow from the boating world and install a shower sump. It's a small tank with a pump and float valve that can sit below the shower and pump grey water back up to the top of the grey tank.

When I constructed the replacement trailer frame I found an appropriate location for a shower sump. I added a small platform between the bellypan and the subfloor just rear of the grey water tank. Shower sump pumps generally are not self-priming and need to pump uphill with no possibility of a dip in the line to the grey tank. So it needs to be located close to the grey tank to avoid a long run that might sag. I also needed to plan for periodic maintenance (or replacement), so I'd need a large hatch in the floor that can support people walking on it.

Shower Sump located near rear of Clipper

After a lot of research I chose a Rule 98B shower sump. It's been around a while and is widely used, fits in the available space, has more than sufficient pump capacity (800 GPH which should more than handle ~180 GPM from a standard RV water pump), and appears to be more serviceable than other manufacturer's models. There are spare spare parts available for the Rule 98B and I plan to buy a set to have on hand.

I was a bit concerned about pump cycling hysteresis from grey water running back into the sump after the pump stopped. I measured the pump cutoff volume (it can't pump 100% of the grey water from the sump) and the pump trigger volume and then compared that to the volume of the pipe from the sump to the grey tank. There is a lot of margin between the two so I decided that pump cycling wouldn't be an issue.

Rule 98B Shower Drain Pump System

I am a bit worried about water damage from a sump failure so I added some mitigations. First, one of the nice things about the Rule 98B is the seal on the lid - not all sumps that are available have this. Second, I mounted the sump in a small stainless steel overflow pan similar to what is done with water heaters. Third, I ran the sump overflow port to a drain point below the bellypan. The overflow port is not a standard size so I needed to find a barbed hose connector that was close in size and then ream it out to fit the overflow port. Finally, I'm also planning to install a simple water detection alarm in the overflow pan so that I'll be alerted if there is a spill.

I plan to have the sump pump switched on with the same power switch used for the fresh water pump. Currently I'm planning to run a 12VDC control switch to a 2 circuit relay that will provide power to both the Rule 98B and the fresh water pump.

I found an aluminum boat hatch trim ring that was large enough to provide room for service and replacement of the sump when/if needed (I don't recall where I sourced the trim ring). By sheer luck the lip of the ring is about the thickness of the vinyl composite tile (VCT) so it can sit flush with the tile when installed. I made a hatch cover using a scrap of the Advantech subfloor trimmed to fit using a template I made from the hatch ring. I covered the hatch with leftover VCT from the flooring. Once I installed the VCT I needed to trim the bottom edge of the hatch so that it would sit flush with the floor. I coated the bottom of the Advantech hatch with penetrating epoxy to seal it from any moisture coming from the sump.

For now the hatch cover sits snuggly enough that I'm not going to install a latching or retention mechanism (I will if I need to). But I did need to install a means to list the hatch cover out of the floor-flush recess. I found some stainless steel "hidden recessed furniture handles" on Amazon that sit flush but pop up a pull ring when you depress a tab. I used a router to counter sink these into the hatch cover so you can pull it out when needed.

Flush Hatch Pull

Shower Sump Hatch Installed