The manual that I have says that your 6 hp Tohatsu may be on its side with the tiller down only. For some reason, the 2.5 hp Tohatsu is the other way up. The diagrams on p. 28 show how not to do it. The motor on its side is tiller up which is wrong. Memorize: tiller down
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This is to prevent oil draining from the crankcase into the cylinder. When I bought my motor, the mechanic said that if you forget and get oil in the cylinder, the motor will be difficult or impossible to start. You have to pull the plug and pour out any oil. Clean the plug if necessary. Top up the crankcase and it should start.
Hope this helps.
BTW Tohatsu makes the small motors that Mercury and Nissan relabel.