Help! Water leak

A few more details would be helpful in troubleshooting:  where was the water spotted on the floor?  by the shower? by the kitchen sink?, You state that the plug cap was removed - do you mean the one on the FW tank or somewhere else?  You are hooked up to your home water supply and state "it's still dripping slowly" - what and where is this dripping slowly?  

The three main areas I would search for a leak on a 171 are: 1) under your kitchen sink - while pressuried run a paper towel over the H and C supply lines, also the trap under your sink and see if there is any wetness on your towel and running over each of the above areas.  2) remove grill under the door that leads to the bathroom/shower and shine a flashlight to where the trap is - look for wetness or drips under the trap - sometimes that can come loose - easy to fix by tightning the screw bands on the plastic trap.  3) Go to your HW tank and inspect to make sure it is all dry - especially the 1 1/16" drain plug and the lever that opens the vent above, if that is leaking quickly open and close - the gasket could have dried out over winter and needs a bit of lube/water to make a tight seal.  Stand back when doing that procedure if pressurized - a lot of water can escape in a moment.

Should have no leak, no drops, nothing.  The low point drain caps either have an o-ring or rubber washer that is either dried out, distorted, or cracked and needs to be replaced.  Go take the part with you to a hardware store and get the part replaced.  Are you located where it never freezes I hope because if you do, there may be more 'leaks' in store in the future.  Sounds like maybe not as you stated you have no other leaks - - that is a good sign.

May you have a blessed Resurrection day as well !

There has to be a check valve of some kind between the tank and fresh water feeding the whole system.  My guess is it may be leaking.  I would leave the drain cap off until you find that valve.  I have never looked but would think it would be near the pump.  Video on youtube says to fill the tank, run pump for 10 min, and that fixed his.

Good Luck