Jim's got it right, cept the jar contained mixed nuts.....seemed appropraite
He's also right bout the routing, off the filler neck to the trunk puke can....the engine crankcase is vented to the oil tank.
For a futher explaination:
For a street machine, it's not really required. Venting to the carbs works. I've seen the venting done to a breather filter right off the neck to the engine room.....that gets messy. My puke can stays dry durring normal use.
For more strenuous use,the catch tank becomes required. Rather than carryng just mist from the crank case, it often carrys "lumps". With high G forces, the stock tank allows the oil to slosh around...even tho it's baffled. Couple that with the greater air movement from the crankcase at high rpms, oil lumps get blown into the catch tank. Prolly some aeration going on in there, also, increasing the volume
I've overflowed the thing....and it will hold more than a quart. I've found if I keep the oil level half way between the dipstick marks, I'll get a couple Oz. in it after 4-5 AX passes. Either way, you don't want that much going thru the carbs or injection system.
Prolly more than you wanted to know, eh?