Great thread. I have a couple.
radiator grill cleaning. I discovered this by accident when doing our bathroom one. I used a wooden cuticle stick inside a damp microfibre cloth. The stick was slim enough to get into the gaps and get all the muck out.
green gunk on trampoline. I did ours last year and used fairy liquid and stiffish brush and hosed it all off. It worked really well. On a couple of stubborn areas I used cream cleaner.
wee stains on mattress. Yes, bleurgh. If you clean the mattress as usual with bio powder etc, then it dries and leaves a brown ring, try the following. I did it on DD's mattress on a dried stain and i couldn't beleive my eyes.
You will need 3 % hydrogen peroxide, from the pharmacy, fairy liquid and bicarb of soda. Put the hydrogen peroxide into a spray bottle with a drop of fairy liquid. Sprinkle the stained area with bicarb - use a seive if it's lumpy. You are aiming for an even layer. Agitate the bottle a little then spray onto bicarb. It will froth and fizz. Go away and come back 15 minutes later. The brown stain will be gone. Seriously. If there are any stubborn areas, repeat and when it's fizzing use a brush to scrub the stain a little. You'll need to vacuum off any bicarb residue when dry.
prolonging cut herbs. This was on Mary Berry Cooks and does work. I've only tried it with coriander so far. Put the bunch of herbs into a glass of water, cover the whole lot with a bag/sandwich bag. Lasted for over a week and no slimy coriander in the fridge drawer.