I have three BRIGGs 4920 1.5 gpf toilets in my 1995 home which get clogged easily. However, the inside shape of the bowl outlet is strangely enough somewhat rectangular. Therefore, none of the 4 plungers I’ve been able to find can seal against the bowl and thus they are pratically useless for clearing these toilets. Is there a (rectangular mouth?) plunger made for these kinds of toilets that are effective or is there some other solution to my problem (short of replacing the toilets) ?