Type in Sandshrimp gun on the internet. The Steelheaders website is the link to show you what they look like and even how to make one. They are not the same as a clam gun. It's easiest to suck the shrimp out of their hole if you are in 1/2" to 1" of water. Just follow the tide in or out. Put the end of the gun about 6" into the sand and pull the handle. The water will allow the pump to work to it's full potiential. It can be done without water but it's alot more difficult. After you pull the handle and fill the tube with sand and hopefully shrimp. Push it down while swinging the tube to the side. This will expel the material onto the ground without making a pile. Easier to see the shrimp. Then put the tube back into the same hole and do it again. The second time is sometimes more productive than the first. I have pulled as many as 8 shrimp out of one hole by doing it this way. I found the larger shrimp to be further down in the sand. As far as knowing the difference between shrimp holes and clam holes. I couldn't tell you. There will be a million holes in the sand at low tide. I only found one or two clams when I went last time. I'm not sure where you plan to go. I went to Garabaldi bay across from the Coast Guard Station. Tillamook Bay is loaded with em. Seaside where the river flows into the ocean is a good spot as well. About 12th street and down a little farther. Hope this helps.
One more thing I forgot. If you want to buy one they are $20.00 bucks at fishermans. It's almost the same thing as the one on the internet. Works like a champ. Good Hunting, since saying good sucking wouldn't sound to good.