Backwater valves, furnace drains, and vent pipes

I'm having a house built and I got a picture of the drain pipes in the basement prior to pouring the slab, and it looks like this:

The left blue circle is a floor drain for the furnace, the right blue circle is an unused 3-inch stack, the left red circle is a 2-inch vent, and the right red circle is a backwater sleeve. The line drains toward the top of the picture and out to the sewer.

The builder installed a furnace and placed it such that it didn't cover any of these pipes:

The placement of the furnace would have blocked a wall I want to put in to finish the basement later, so I asked the builder to move the furnace, which they did. However, as you can see in the next picture, the furnace is now covering the two red-circled pipes which were cut and capped, and the builder modified the unused stack to make it a 2-inch pipe:

I asked the builder about this and was told that the backwater sleeve didn't need to be exposed, the vent pipe was cut and...

Frequently Asked Questions about Mainline Backwater Valves

Q: How much slope is required in a drain line in order to use a backwater valve?
A: In all installations, make sure the slope is adequate. It must be at least 2% (or 1/4" per foot) to insure proper operation (NOTE: this requirement does not apply to SF [Straight -Fit] and ML-FR-4 valves).

PLEASE NOTE: The Adapt-A-Valve takes up 6" of run in your line and the outlet is 1-1/2" LOWER than the inlet, so in just 6" the level of the pipe at the outlet side needs to be 1-1/2" lower. The Fullport Backwater Valve takes up 12" of run in your line and the outlet is 3/4" LOWER than the inlet, so in just 12" the level of the pipe at the outlet side needs to be 3/4" lower. Depending upon the amount of slope in your line (2% minimum is required for proper operation), you may need to replace several feet of pipe downstream from the valve to average out the "loss" of fall built in to each valve.

Q: Are...

Many thanks to you guys for sticking with this thread.

Regarding the venter trap: I made sure this is full of water. I filled it myself by disconnecting the venter and pouring water into the tee until it overflowed through the drain tubes in the trap. The problem can't be in the trap anyway; the water is never getting that far. It's overflowing into the venter and then into the tube to the pressure switch. If the venter were stronger, it would propel the water into the tee and then into the trap (and undoubtedly that is happening with some of the water, but other water is getting into the pressure switch and some is just leaking out of the joint between the venter and the tee).

Grady mentions an O ring and a restrictor plate. There is a disk about 1/8" thick, and it goes on the flue collector box where the venter attaches. I thought it was plastic, but this must be the ceramic plate they talk about in the manual. Just as ecman describes, it's not attached to...

What are Backwater Valves?

A backwater valve is a one way flow control valve installed in a drainage system, that under normal conditions allows the waste water to drain out of the system, however if a reversed flow of drainage water should occur, the valve will be forced closed and protect the interior of the building from sewage backup. Every year thousands of homes are flooded with raw sewage and storm water, causing millions in damages that could have been avoided with properly installed backwater valves.

When are backwater valves required?

Backwater valves are required to protect fixtures and drainage openings that are installed below grade; such as in a basement, where the possibility exists for the municipal sewage or storm water systems to become overloaded and force waste water back through your sewage drains. Backwater valves are also required on any subsoil drainage pipe that connects into the sanitary drain, to also protect it from sewage...