what worked for us - I don't know if it will work for you - was I threatend to go into the bathroom with the boy and shower him myself, scrubbing his back and anywhere else. He had the option of wearing his swimsuit (Speedo briefs, known in Australia as "budgie smugglers") but I didn't make that too obviously known, I did let the boy think I was going to see him in the altogether if he didn't wash himself.
Same thing with hair washing.
Mind you, difficult child 1 was hydrophobic, very. He literally went years without washing his hair.
Something else that has got the message through - as teen acne kicks in, I get picking and cleaning. And the longer they stall washing their hair, the worse the skin on face and back will get. So to prevent Mum having plenty to attack, they need to keep their hair clean and skin clean.
Persuasion is always best, of course. Finding what the problem is (sometimes it's simply inertia, they're busy playing acomputer game or reading a book and just don't want to move) can help. For example, difficult child 3 has been difficult about showering lately; he said last time that he wants to go back to having a bath instead of a shower. That is what worked for difficult child 1 as well, espeically with the hair washing. it gave him more feeling of control over where the water goes.
We have a large bathtub and I laid in good supplies of bath bombs and bubble bath. NEVER use soap in a bathtub, use bubble bath instead. Forextracleaning, put shower gel or bubble bath onto a sponge. Soap is made from fat, it will leave a ring around the rub even if you're washing a clean body. If you have bubble bath, soap will kill the bubbles really fast. In fact, if you overdose your washing machine or dishwasher, just dunk a bar of soap in the water and swish it about for a minute, the overload of foam will die down fast.
Bubble bath, shower gel and shampoo tend to be detergent-based, not soap-based.
I also insist on deodorant being put on immediately after a bath (I get the super-strength stuff, 22% aluminium chlorhydrate, for teenagers especially boys). We don't want to waste a wash.
Clothing that has been on a sweaty body should not go back on to a clean body, or the sweat smell transfers (even if he puts deodorant on). But trying to clean up teen male sweaty clothing is tricky.
Here's what works for us -
1) pre-treat clothing with white vinegar. Buy the cheapest industrial-grade white vinegar, not your best salad stuff.
2) if it's really bad, put the vinegared clothing into a warm (not hot) pre-soak with an enzyme soaker. Some laundry detergents can double as pre-soak. Findwhat works.
3) Wash the clothing, possibly in a load on its own (smells can transfer to non-smelly clothing). Wash in COLD water using a cold water detergent. If you hot wash, you risk cooking the smells in. Smelly sweat is a protein, hot water cooks proteins.
4) If you need to, repeat these steps. You should only need to do this if it's REALLY bad; I've successfully cleaned the absolute worst stuff by the third wash.
Once we were into a routine, one wash was enough, often I didn't need the pre-soak. But always we use the vinegar. We kept a pump spray bottle full of vinegar in te laundry for fast & easy application.
You get into a routine of throwing stuff in the laundry and splashing on the vinegar as you do - it doesn't matter if it's days before washing day and it dries, because the low pH is in the clothing and as soon as it gets wet in the wash, it is active again.
We stopped the "basket in the room" routine, because nothing was going into it a lot of the itme; and when it did, it never made it out to the laundry. Instead we organised for the kids to either toss their laundry outside the bedroom door or then to walk it further and put it into the laundry tub. That's the point at which to add the vinegar (it will even remove sweat stains, even long-term ones, although the pre-soak detergent helps there). It was messy and seemed undisciplined to have the laundry outside the bedroom door, but at least it was out of the room and not stinking it up. And as it turned out, it became the first step in training them to first put the dirty washing in the laundry themselves, and finally to do it themselves (now they don't live at home, except for difficult child 3).
it shouldn't matter if you have a different routine to foster mom, because kids DO quickly learn "different strokes for different folks" but if you can collaborate with foster mom you might find a coordinated approach works more effectively.
But if you do as we did and "offer" to scrub his back for him and wash his hair for him, be prepared to follow through.
I've also sent my kids back in to wash properly, if they came out and 'forgot' to wash hair, for example.
Another issue to consider - sensory problems. If he has sensory integration issues then washing himself or his clothing can be a HUGE hassle. We had this with difficult child 1 - while he was at school I would swoop on his room, strip his bed, collect his pyjamas and any clothing I could find, wash the lot, have it dry and back exactly where it had been, by the time he got home form school. But instead of being grateful for a clean-smelling bed he was upset. His bed and PJs didn't smell right, he said. They didn't feel right, either, and he couldn't get to sleep that night because things smelled wrong.
Of course that's tough cheddar, difficult child 1 had to put up with this and learn to adapt to the smell of CLEAN, but this was a big factor in his resistance.
Getting interested in girls was a big incentive to cleaning up. Also when he was seriously depressed, we had a lot more trouble getting him to wash or even to look after himself. His school would ring me and complain, I explained I was doing my best but I was worried too. Antidepressants helped.
It's summer where you are. That cna add to the smelly problem but you have access to something in summer thta you haven't got in winter - the garden hose. I have threatened to take him outside and hose him down, as if I was bathing the family dog in the wheelbarrow.
Agian, whatever you threaten, you have to be preared to follow through. So don't threaten anything which is likely to provoke a major meltdown.
Incentives can work even better, if you can find something that is sufficient incentive. For difficult child 3, it was bath bombs. easy child 2/difficult child 2 insists on such complete control that she bought herself a digital cooking thermometer and uses it to get her bath water to EXACTLY 42 C. Having control can help a lot. Offering some sort of bribe (an activity together, for example) as incentive after he's washed properly, can help.
Marg