Get a strainer or colander, put it over a bucket and scoop the grain/water in to it. When the strainer is full, dump it back in and repeat until there is minimal water left. Then dump the bucket in to the boil kettle.
Try sparing as you normally would. If it doesn't work, repeat the process - scoop grain and spare thru the strainer.
This happened to me once, with grist that had lots and lots of oats.