longbob.
Good choice, the newer (there seems to be two versions) Grub Stake has the flared mouth, boil box and ramp riffles but not the Abyss trench riffles. Still the riffles are deep and you won't be loosing any gold. Yes the rain is a curse for some and a blessing for others as it churns up the gold and redeposits it hopefully where we can find it....
If your digging small gravel off the bottom (bedrock) of a creek there is no need to classify with a sieve, just slowly drop the material onto the front of the sluice and the water will move it along. But, if your digging dirt from the banks then you will need to classify and the small "Garrett Gold Pan Kit" has everything you need aside from a bucket to carry it in and your shovel.
You will need a bucket as your sieve fits into the top of it or you can use the pan, but most of us use a bucket. Sieve sits on top (in) bucket, pay-dirt goes into sieve, add water, more pay dirt, more water, check the sieve for those big one ounce nuggets then flick the rocks away (you can always run a detector over them later), repeat the process until the bucket is mostly full then ladle your 'concentrates' slowly into your sluice the water-flow should be fast enough so that by the time the ladle is empty the mouth of the sluice is too.
Repeat the process until you run out of concentrated material then you can carefully wash out your sluice into the pan and pan for gold.
Have fun and if your on the gold, remember to take some happy snaps and post them up for us to see!