Cleaning/Filling Second Hand Tank ?

AM
If you have a hand-held steamer you could use that. We have one, and it is a really useful tool to have around the house.

You could also use a spray bottle and then wipe over, or even a squeegee if you have one.

Use a hose/spray gun to wash the sides of the tank down to the bottom. Then siphon the water out. Repeat a few time till you are satisfied you've got everything off the glass inside the tank. You won't get the last bit of water out with a siphon though, the only way I've found to get that out is to soak it out with towels. We keep old ones in the garage for anything messy.

When filling up, add a couple of inches of water, leave overnight and check for leaks. If it's OK, add a couple more inches, leave overnight then check for leaks and so on till it's full.
Warning: if you use just cold tapwater it will be so cold you'll get condensation on the outside wherever the water is in contact with the glass and if it runs down the tank this could fool you into thinking the tank is leaking. Use warm water!

warm water and aquarium salt is all that
is needed to clean an aquarium if you feel that
is not enough you can use some methylene blue
or malachite green or some potassium permanganate
any of these will disinfect your tank you can use one of
them green plastic pan scrubbers as well i know its old school
but always works for me on the out side of the tank you can use
meths and old newspapers shine the out side glass up a treat 

Well tank is very clean now, the Bicarbonate of Soda did a good job, and i gather it is put in some tanks in small quantity for some reason for Ph balance maybe? so not harmfull, Just going to give it another rinse and siphon and then off on substrate hunt lol. Thanks all 

Thanks Sue, i think another rinse will do it