Bathroom – How to Fix a Bike Cable Type Drain Stuck Down

Can you provide any pictures or a more detailed description?

I presume these are normal threads and you are trying to turn the wrench counter-clockwise to loosen, right? :-)

It sounds like there may be corrosion involved, which will make it difficult to loosen. It could also be good old-fashioned pipe-dope that is thoroughly set and hardened.

A longer handle on that wrench might help (Archimedes, levers, etc.).

Also, impact can help a lot. Tapping it with a hammer while trying to turn it might do the trick. Or pounding the handle with a hammer in a counter-clockwise direction might do it.

Once you get it to start turning, the rest should be easier.

Of course, depending on your tolerance for replacing part of your plumbing if it breaks, enough raw physical force can solve a surprising number of problems...

I believe you are over estimating how much hot water is needed to fill the tub. It will be filled below the overflow drain that should be built into the tub. You can reduce the total by the size of the person getting into the tub. And most importantly you can reduce the amount of hot water by any cold water you include to regulate the temperature, perhaps you are only using 2/3 hot water to 1/3 cold water.

The important question you'll want to determine is how quickly the water heater can regenerate a full 50 gallons of hot water because you may want to heat the bath back up after a while, or use hot water for some other purpose after taking a bath. If you find yourself near the threshold of available hot water, you may find it easier and cheaper to increase the temperature of the hot water in the existing tank, rather than adding a tankless water heater.