Source of water in drain

[Cherper]

Hello everybody! I’m a somewhat seasoned rental property owner. I can do most plumbing repairs but this has me stumped. I have water backing up into tub and toilet causing both to run over. If I shut off main water supply, the tub and toilet drain. Perhaps a little slow. Typically I would look at drain under these conditions but here’s the rub. As soon as I turn on water main, the water immediately backs into tub and toilet rises until it overflows from both. There are no faucets running or toilets trying to drain. How in the heck can the drain get a supply sufficient to overfill the bathtub? So ok, I may have a clogged drain, which I’ll auger out today but the bigger question is where is water coming from? Last month my water bill was $930 when it usually runs $200-$250 a month. I only have one main coming into basement. Please help as I am stumped.

 

[Sylvan]

You differently have a stoppage possibly main trap or main line

If you have a water meter check the dial to see if it is moving Check your toilet tanks by shutting off the water to the tank and look inside come back a few hours later look again as there could be water loss through the Douglas valve

 

[Sponsor]

 

[MACPLUMB]

Your toilet flappers are leaking water, running 24 hrs a day 7 days a week will drain a water reservoir in a month, !
you can get dye taps at any hardware store drop in tank and see if it starts showing the bowl

 

[Reach4]

As soon as I turn on water main, the water immediately backs into tub and toilet rises until it overflows from both.

Wow.

Turn off all available valves, including the inlet to the WH, to see if the problem appears if you then turn on the main valve.

If the problem continues, maybe let things warm up in the hot part of the day. Open the main long enough to get the flow without overflowing. Check the temperature of the pipes at various places. Expect the pipes carrying the water to be colder.

Whether you use your hand, upper lip (most sensitive temperature detector on the body), FLIR camera, or an IR thermometer is up to you. IR thermometers can be pretty cheap these days.

If not successful, consider adding more valves to aid in the tracking.

 

[Sylvan]

Your toilet flappers are leaking water, running 24 hrs a day 7 days a week will drain a water reservoir in a month, !
you can get dye taps at any hardware store drop in tank and see if it starts showing the bowl

If you don't have dye use instant coffee