I have an exhaust fan (antiquated as it is)in the main bathroom and want to put another in the smaller Bath. My question: can I use a "Y" connection to hookup the new fan to the old exhaust that vents outside? Another ?, should I seal the floor tile in the shower after grouting or is this not common practice or adviseable. Thanks in advance, y'all.

Theoretically there is no problem with the "Y" connection, however, you MAY experience a slower removal of moisture if both showers are operating simultaneously (or you may not).

The grout should be sealed every year or two with clear silicone sealer. I cannot speak for the tile not knowing what type it is, but it is probably glazed so it won't accept the sealer anyway.

Thanks, Doc.