Plumbing – Fixing porcelain sink with crack and rusting drain

This might not be the answer, but for reference here is a problem that can occur if the plumbing is not installed properly.

If you look at Fig. 3, this is what a proper drain looks like. You'll notice the orange line represents the water level in the system, the water levels out in the trap preventing sewer gases from entering the sink drain.

In Fig. 1, you can see what will happen if the drain line has to go up before meeting the main drain line. Again the orange line represents the water level in the system, and as you can see the water level is much higher in the drain.

Fig. 2 shows what could happen if the sink was installed lower than the rise in the drain line. The water would never fully drain from the sink, since it would require extra pressure in the system to push the water up the drain.

I wouldn't guess this is the issue in this case; since as you can see, if you opened the trap in this case you would have more water drain than what is typically in the trap.

In a perfect world Fig.1 and 2 would never pass inspection, but as we all know not all plumbing is properly installed and/or inspected. So this could possibly be the case in this situation (given the plumbing was installed by an amateur plumber), but it is doubtful. It would be more likely caused by a clog in the line.

Your vanity plan should have front side doors in line with where the sink is located. Then the drawers should be off to the left or right side where there is plenty of height and space toward the back to accommodate their placement.

There are multiple reasons to not put drawers in the vanity under the sink area:

1. People stand in front of the vanity at the sink. It is extremely inconvenient to have drawers opening out at knee height where the you want to stand.
2. You cannot place any sort of drawer directly in front of the sink and drain because there is just not enough depth from the front face of the vanity to accommodate the drawer. Any drawer placed below the bottom level of the sink would have cabinet face framing running across in front of the cabinet that would make it difficult to make access to the space under the sink.
3. Having drawers in the space under the sink will restrict access to the water shutoff valves keep it from being possible to quickly inspect the drain area in the case of suspected leaks.

So I really recommend that you not put drawers in this part of the vanity cabinet. You will find plenty of things to store in the area under the sink behind the doors.