Help to get sweat smells from teenage boys clothes.....

[doradoo]

They seem resistant to usual washing - even washing twice before wearing again.

Any tips and tricks to get the smells out - or do I need to dump the t-shirts and start afresh?

Rub washing up liquid into the sweaty bits before putting them in the washer make sure you use bio washing powder not none bio.

Make sure you are using enough detergent: check the pack instructions.
I use 2 Persil capsules in a wash, as it's a large capacity machine.
You might also need extra if you are in a hard water area.
Also, Lenor Unstoppables are nice for extra freshness.