Bait pumps are superb, if you target the right type of worms (runnydown and yellowtails) Their casts are always small and very neat in an almost perfect spiral. I almost gave up with mine, but stuck at it, and now I have the confidence to take it, without taking a fork for back up. Don't worry if you 'pull' a worm up that has burst; run the guts out of it and freeze the worm (excellent bait). In all honesty I tend to do this with most of the intact yellowtails and runnydown anyway, as they are notoriously hard to keep in tanks, often 'bursting' themselves, and contaminating the water.
Don't give up mate. Take a fork as back up, but try various methods when pumping over casts. Some people swear by pumping directly over the cast, others prefer to star about 3" - 4" away from the cast and go in at an angle.
However the secret seems to be keeping the pump steady whatever angle you go in and maintaining as much suction as possible.
If you haven't got one yet, my advice would be to go for a slimline model. I started off using a thick version, and found it more back-breaking than digging !
Hope this helps and good luck.
BAZACODBASHA