Don't understand what you plan to do. So if you want your home mail server been reached after filtering the mails with PMG, you just need to setup PMG to fetch the mails on port 25 and then need to add your domains and set the destination server to your home mail server. If you want to route outgoing mail through PMG, you need to set up on your home mail server, that outgoing mails should go through PMG on port 26 and let PMG do the mail job. If you install the gateway outside your home lab, you need to direct the MX to PMG and then to your home server, take sure, that your home server only accept mail from PMG, otherwise some spammers will directly still deliver spam to you.