TBH passive (unpowered plastic Y-type) splitters are not good for digital TV since they reduce the output signal and are usually unshielded. The normal way to connect the aerial to the TV using the Toppy is to use the pass-through RF Out connection.
The connection methods are described much better in the rewritten updated manual
http://www.toppy.org.uk/documents/58...nual_Rev.4.pdf (Forget the printed one!). Remember to make sure that RF Loop 2 Out also connects to RF In.
There may be some slight degradation of signal but it shouldn't make any difference in most cases.
If you are in a fringe reception area for digital TV, then instead of the pass-through connection you might need an active (powered) distribution amplifier to connect separately to the Toppy and TV.
If you are seeing interference when connected via the Toppy then the next step is to temporarily connect the aerial lead to the TV directly. If no interference is seen then there is the possibility of the Toppy's analogue output channel might be interfering with your local transmitter's broadcast analogue channels.
To cure this, use the Toppy's System Setting to change the RF output channel to a low or high value e.g. 21 or 69.