T5 Trident, water tank taps/240v mains plug.

Advice appreciated on :
a) drain taps from water tanks - there are two on the nearside, and one right at the rear of the tank underneath...am I right in thinking that the front nearside one is the waste, the rear one for the fresh ? and would the third at the rear be for draining a hot water system (not fitted on mine)
b) the mains 240v plug - this is the smart black and chrome plug with surround, next to the matching 12v plug, alongside the control panel. On mine, the 12v plug is slightly loose, but the mains plug is quite loose...can't see any obvious way to tighten them up, presumably the surround has to be removed, but I don't want to risk any damage to anything until I'm sure about what to do.
c) The Eberspacher diesel heater is not working (should have tried it before buying !) On ventilation setting, blue light comes on and fan starts and runs. For heating, the red light comes on, then...nothing. Presumably the heater is sealed away underneath the van, with nothing to fiddle with ?
Thanks for any advice.

c) If you're trying this with external mains not connected, what state of charge is your leisure battery in? If the leisure battery voltage is too low the heater may simply refuse to start, as the fuel pump and ignition takes a lot of current initially.

problem solved, thanks....have just connected to mains at house, and heater fires up and runs normally. battery meter was showing a "good" yellow charge, but was obviously not enough to start the heater.

...on further investigation as to why the Eberspacher wouldn't start up, I found that the leisure battery, although it doesn't look really old, is only rated at 68AH - and that the cells are deficient of essential fluid