Radiator flushing on the GU 4.2????

Okay; so here's the latest decision I've made to try to curb the overheating 'trol......

Following everyone's advice a few days ago (thanks everybody), I've decided to buy a new thermostat (it's says it 76.5 deg) and instal. Unfortunately, the gasket the Nissan bloke sold me doesn't look like it'd fit, so I couldn't do it this weekend. (They sold me one with 4 holes in it which is sort of rectangular in shape but with one end cut off at about 45 degrees, whereas the thermo housing is round shape with 3 holes in it).

I've also decided to flush all the coolant out and replace with pure rain water + 2 bottles of REDLINE's product called "Water Wetter". I've ordered the pink one (no smart arze comments you blokes!!!! hahaha) which is for both diesel and petrol vehicles and contains a rust inhibitor. The blurb says that it cools much better than water on it's own and even better than a coolant-equipped engine. From what I can gather, commercial coolant actually detracts from the cooling systems ability to do it's job...... I reckon if I've been guilty of putting too much coolant concentrate in the donk and this could be part of my problem.

Anyway, I know there is a drain plug somewhere on the back of the block somewhere. Does anybody with a 4.2 Nissan know exactly where this plug is and whether it's best to access it from above, or below the motor. I think it's somewhere mear the turbo, but if anybody can confirm this I'd be grateful.

I'm also unsure how to know when the flushing process has been completed and if all the town tap water I use to do this flushing job will get itself out of the system, or will I need to "waste" a certain amount of rain water to flush the krappy town water out before I fill up??

Thanks again for your responses....remember, the sooner you all can help me solve this problem, the sooner you won't have to put up with my long-winded, silly questions.

Cheers everybody,

Roachie.