Info Rusty fuel tank

OK so I've done an experiment on both my tanks to de rust and see the results pictures to follow
Tank 1 I used the reverse electrolysis method is flush the tank with soapy water then de gunge the tank with hydrochloric acid (drain cleaner) then set up a battery charger , metal rod ( I used an old draw slide ) firstly fill the tank with warm water 3\4 full , mix up soda crystals 2 spoons per gallon in a jug with water disovle it then pour it in the tank top off with water ,place the metal rod in the filler hole making sure it doesn't contact the tank ( i used elec tape the bottom use a cut off bottle lid opening for filler hole )
Connect the charger neg to tank ,pos too the rod and switch it on
This was left for a week then rinsed with soapy water
The tank was virtually rusty free when dry'd but within a week rusty again so
Tank 2. De gunged with drain cleaner over night
Poured 500 ml white vinegar into the tank and a few handfuls of fish tank granite gravel in swill about for an hour or so empty and flush with soapy water then after an hour it was there was still rusty deposits so of too the wholesaler for 20ltrs of white vinegar poured straight in to the top ( note the tank doesn't get completely filled as I found out ) set the tank on the floor for 6 days moving it son all the surface areas were in contact with the vinegar for a bit of time
Now it was time to check results completely rust free on empty ,
OK now here's the fun part flushed the tank ,soapy water till water comes out clear ( not so good in the bathroom with a shower ) then rinse with BBQ fuel to remove any slimy sludge
The poured in some washing machine de scaler ( I used kilrock big w ) but any will do that contains phosphoric acid 200ml and swirl about ten minutes
Don't get it on your paint is supposed to be safe but the splashes dulled it not bothered its going to the blaster next week and don't get in on your skin it burns
Now as for the progress tank 1 has heavy rust again so the vinegar used before will be going into that because it needs it
Tank 2 very clean now with very slight surface rust prosume were I didn't flush with BBQ fuel long enough / swirl the descaler
Not really sure as to tank liners yet seen mixed reviews on them all and so any guidance would be gratefully received

 

ok tank one as you can see suface rust is back and the filler cap is only on there so i didnt loose it (have got a brand new one will see if it cleans up in the ultrasoniic )

 

tank 2 these were taken half way threw drying stage hardly any rust at all so for the price of £20 all in

 

thanks grey ive just ordered por-15 metal prep and sealer so now do i send tank 2 off for blasting before or after i wonder