Can I use a plastic basin positioned near joists to compensate the lack of slope in a ceiling condense drain?

Question

Is this a design that is acceptable?

Basically I am building a small box that will collect water pumped up by the condense drain. I will put this up in the ceiling in the furnace room just between the joists. The pump will pump the water in the box. If the 1/2" does not have a proper slope this will compensate for the lack of it; as the water level increases in the basin it will force the water to drain through the pipe.

This is intended to reduce the stress on the water pump which is currently having to push twice to push the water surplus through the existing setup. This is partially because I went all the way to main drain with a 3/8" PVC tubing and I think that is bad. When the pump stops the water trapped on the vertical segment between ceiling and joists level has nowhere to go and it drains back in the pump collector box.

That in turn makes the pump start again and the cycle repeats till sufficient amount of water is finally pushed through to stop this even when the water is coming back.

The alternative, in case I manage to give it a mild slope is to use this setup Update: NOt sure what is causing the water backflow that I am seeing at the bathroom end where the drain will be (for now I am using a bucket to test this) The pump seems to have a backflow preventer as there is water in the vertical segment

Update2: I think what is happening here is this. When the pump stops there is a hump at point ❶ in the last picture. That water will flow back and it creates negative pressure and that is causing the water movement that I am seeing in the tub despite the pump having a backflow valve

Answer 1

Assuming this is an open system draining to outdoors (not to sewer) you don’t need the basin. Your second drawing takes care of all you need:

• The drain pump line is as close to vertical as possible, making it as short as possible, hence minimizing the amount of water in it. If the backflow fails or leaks it won’t be of much consequence. (Assuming the volume of water in that line is much much less than the volume in the condensate pan).
• The main discharge pipe is at its highest at the end where you inject the water. That is the only function you need from the basin, and you get it without the basin.
• The main discharge pipe is vented where it meets the pump line so there will be no siphonage

If on the other hand the volume of water in the vertical riser from the pump is not much much less than the volume of the condensate pan, you need a different solution. You either need to make sure you backflow preventer at the condensate pain is absolutely drip tight, or you need to discharge to a much bigger sump, at floor level, where my above assumption will hold.

Answer 2

no you can't do that. if it connects to the sewer it needs need to either be sealed or have a trap.

Use a fatter pipe eg: (inch and a half) , support it properly and fit a proper trap on the end. the flow rate is low enough that your run can self-vent but you will need 1:100 slope

maybe find somewhere else to discharge the condensate. it's basically pure water, it doesn't need to go into the sanitary sewer.