A crude Scottish expression for a sex act involving an individual (more commonly a male) either receiving a finger in their anus during foreplay or alternatively as an form of masturbation, with the crucial addition of bubbles. It is commonly referred to as simply a 'soapy pokey'
'Aye, got my first soapy pokey bum wank the other night.'
'Gies a soapy pokey!' (humorous)