How to drain the colorifier?

[nightowle]

The horizontal calorifier in our 35E has a leaking temp/pressure relief valve (seen here with the blue knob) which I need to replace.  It is more than 1/2 way up the tank.  Our boat setup has an fwd and aft water tank valve for switching tanks but no "on/off" at the tank outlet.  I'd like to drain just the colorifier down to a level below the relief valve.  I fear that it will just be replaced via the freshwater tank as I attempt to drain water.  I could remove all 40 gallons of one of the tanks via a faucet but that will have the water pump running for quite a long time.  With all the water tubes and exhaust all running in the shallow area below the aft berth, I can't easily place a large enough bucket, either.  I'd like to keep the water from once again permeating all through the bilge.  Any ideas?

[Rampage]

I routinely empty the tanks at the end of the season by running the fresh water pump until the tanks are empty. I’ve got a 16 lpm pump, so it takes about 10 minutes to empty each tank. Doesn’t cause any harm to the pump.
But you don’t need to empty both tanks, just one.
In addition, the calorifier is filled by the water pump: it won’t refill as little or no water will bet past the pump if the pump is switched off. You’ll still have the contents of the calorifier to deal with but there’s no way to reduce that as the hot water exit is at the top of the tank.

[nightowle]

Thanks, Rampage.  That helps a lot.

[PEA-JAY]

Close cold water supply. Switch off 12v pressure pump and 220v heater and let water cool down. Release any pressure via hot water tap. Undo hot water outlet on calorifier  and insert a smaller diameter plastic pipe. Syphon off to a shallow pail or jerrycan even lying on its side a little at a time.
Hope you manage.

[nightowle]

Thanks, Pea-Jay, but unfortunately there isn't a cold water supply shut off.  Only a levered valve to change from forward to aft tanks.

[symphony2]

Once you have drained the tank, not difficult to fit a shut off valve to the tank. I did this when I replaced the forward tank. The tank had a BSP outlet fitting that made it easier, but you can fit an in line valve. I have done this in the hoses to the stern shower as mine is the type where the tap is in the shower head so the pipes up to head are always under pressure. Inserted pushfit valves into the hoses in the lazarette so that I can isolate the shower head and remove it in the winter while still keeping the domestic water system full.

[nightowle]

Thanks, Symphony - I should do that.  And the shower shut-off makes a lot of sense too as they always seem to be culprits for leaks.