I just completed my tank. I should have read the posts prior to doing the the tank because I did not dilute my acid. Heres what I did:
1) Removed the petcock from the tank
2) Poured acid into tank
3) Put a handful of rocks/gravel into the tank
4) swished everything around for a few minutes(remember to wear some safty gear, I did and luckily did not feel the pain acid can cause)
5) Poured the acid out into a pail
6) Pour more acid into the tank & Swished it all around
7) Let the acid sit for a minute or two slowly rotating the tank to cover all surfaces
Drained tank & flushed with RO water
9) Flushed tank with baking soda/water mix (I did not really measure it out)
10) Repeat 9 several times (I flushed it out with a baking soda mix two or three times)
11) Flush well with water (I used hose water because I ran out of RO and was not sure if it is better)
12) Washed out with rubbing alcohol
13) Coated with ATF (WD-40 will work as well)
The tank looked good before I coated it with ATF. I will let you know how it looks in the morning.