engine block? Disconnect the hose from the discharge side of the pump and carefully measure the hose diameter.

Now go to the point where the cooling water comes out of the engine. On the Atomic 4, the cooling water exit is at the left rear of the engine at the back of the exhaust manifold. Disconnect that hose and carefully measure its diameter as well.

Think about it
Now before going to the store, think about what's needed. Every hose connection will need a hose clamp
  tell you how long your hoses need to be. Remember you need a hose clamp for every connection.

What's the best way to power the solution through the engine? A cheap way is to buy a Jabsco rotary pump that chucks in to your hand -held drill like a drill bit. Marine chandleries sell them for about $15. But don't hang around too long at the marine store or you'll buy expensive stuff you don't really need. Instead, off to a hardware store for the rest of this project.

For very few bucks, the local hard­ware store will sell you two 5-gallon plastic buckets, a gallon of muriatic
  because this cleaning is going to be done under pressure. A double­headed hose barb will be needed to connect the hose carrying the acid solution to the cooling water hose you disconnected from the water pump. A hose of the right diameter and length will be needed to connect to the cool­ing-water discharge port at the rear of the exhaust manifold. Think about where you'll put the 5-gallon bucket holding the acid solution. Think about where you'll place the 5-gallon bucket receiving the acid and goop coming out of the engine. Those thoughts will   acid (30-percent solution), and hose clamps (at least two clamps for the two-headed barb, two for the drill­pump intake and discharge barbs, and one for the discharge -line connection to the engine). Get hoses of the right diameter for the connections and of the right length to easily reach your buckets.

While at the hardware store, get a female garden-hose connector that fits the acid/crud discharge hose. Also, pick up the right-sized two-headed barb to fit the hose on the engine's cooling-water inlet side.