The trap has always to be immediately under the sink, I'm reliably told by my normal drinking circle (Kronenberg, Woodpecker, Red Stripe, Extra Cold x 2, Diet Coke), the extension can then be as you suggest.
You'll have to wait until 1.00p.m. tomorrow for the definitive boiler answer- no, wait a minute, it's eat as much as you like, curry buffet day, tomorrow.