help with cleaning old carboys

So I got back a 6 and 5 gallon carboys I lent a friend a few years ago.. He did a crap job cleaning it and while I've done 2 hot oxy soaks (24 hrs each) for each carboy they still have crap in them. The 6/gallon still has trub/krausen stuck to it even after trying the brush in it. The 5 gallon has a white film on bottom.

Any ideas on how to get them clean so I can add them to my rotation?

Would a vinegar water solution eat the white away? Maybe its water scale?

Could always try star-san, it is acidic and will involve less work cleaning it out afterward than vinegar (the smell lingers, at least it seems so to me).

Crushed ice and rock salt. Swirl until the worst of it is gone. Be careful not to bump anything.

Cool water and half a cup of bleach. 48 hours later clean and clear. Just needs a thorough hot water rinse afterwords. I clean all my carboys this way. Almost never need to use the brush.

I saw a thread on here about using some acid tub and tile cleaner.. i tried it and that mostly worked.. then I had to rinse it like 6 times.. then I filled with hot water and did another 24 hour OxyClean soak.

They dont look to bad now. I have to check with a bright light to make sure theres no tiny specs still stuck but it looks like I may have gotten it.

3 year old fossilized krausen is no fun to try and clean out. I had to dig out my brush and I never use those things.. typically a 24 hour oxy soak and it looks like new.

I use a PBW solution on carboys with gunk, if it doesn't come off easily or there is a lingering film or haze, fill carboy with PBW solution and let it sit there for a day or two. Dump the PBW in buckets and if the film or other residue doesn't come out put the PBW back in and let it sit for a week or two.